1. Field of the Invention
The present invention relates to a structure for light emitting diode (LED) dies, and more particularly to an LED with a protection structure and a method of fabricating the same.
2. Description of the Related Art
LEDs (light emitting diode) have many advantages such as easily designed drive circuit, DC power use, low power consumption, and ease of application in mobile devices. Due to their compact size, they can also be integrated into devices of medium or small size, or into devices that need to be miniaturized. In addition, with increased RoHS (restrictions on hazardous substances) directive adopted in the European Union, LEDs have further environmental advantages. Furthermore, the products of the LEDs adopting the semiconductor process are firm, solid and anti-shock. Moreover, lights of different wavelengths within the visible light range can be emitted by the LEDs. LEDs are applied to a wide range of uses from indicator lights to other applications such as illuminations and backlight sources.
With conventional light sources (such as incandescent bulbs), much of the consumed energy is wasted in producing the infrared light that generates heat but cannot be seen by human beings. In addition, the working life of the light source based on cold cathode fluorescent lamps is shorter, and a stabilizer is needed for driving the lamps. In such lamps, an electric field between electrodes needs to stimulate mercury vapor for emitting light. Therefore, it cannot satisfy environmental requirements. In contrast, LEDs do not produce heat. For energy saving purpose, LED light sources with long working life are considered a more “green” energy source. There is a huge market demand for high-brightness LEDs.
In order to increase the brightness of the LED, there are two ways. One is to increase the current density passing through the LED, while the other is to use an LED die with large area (ex. 40×40 mil2) to enhance the brightness.
In addition, another method to increase brightness is to reuse the light that is not directed externally. As shown in FIG. 1, the epitaxy structure layer 12 of an LED is formed on the epitaxial substrate 10. A so-called compound reflection metal layer including metallic aluminum layer 20, metallic titanium layer 22, metallic silver layer 24, and metallic tin layer 26 is formed under the epitaxial substrate 10. Generally, the brightness of LEDs can be enhanced by from 30 to 50% with the addition of a compound reflection metal layer.
After forming, the LED needs to be packaged for further application. At present, during the packaging, a die is mounted on a substrate by a silver-filled epoxy resin. This silver-filled epoxy resin with the capabilities of electric conduction and heat conduction is specially used for the die structure of an LED with opposite electrodes. After curing, an LED is mounted on a package substrate by the epoxy resin.
Another method for mounting an LED on a package substrate is a eutectic joint method. As shown in FIG. 2, the lowest layer, the metallic tin layer 26, of an LED can be adhered on the solder layer 30 of a package substrate to form a metal eutectic. The advantages of this metal eutectic method include a tight joint, high pull-push strength, and better heat dissipation.
However, during the soldering of the eutectic solder joint and the extruding process, the solder will climb up along the edges of a die and enter the reflection metal layer. As shown in FIG. 3, the climbing solder 40 may enter the interface between the epitaxial substrate 10 and metallic aluminum layer 20, the interface between metallic aluminum layer 20 and metallic titanium layer 22, the interface between metallic titanium layer 22 and metallic silver layer 24, or the interface between the metallic silver layer 24 and metallic tin layer 26. The solder 40 entering the interfaces between the layers will decrease the efficiency of the reflection and working life of the LCD.
From the above, the die structure of an LED that can prevent the solder from invading the interfaces between layers is needed for the market to overcome the shortcomings of the LEDs of prior arts.